Re: How smart is 'seek $fh, $pos, 0'?

Absolute seeks (forward) are (nearly twice) faster than relative seeks from the current position. (Maybe it has to do a tell to find out the current position before relative seeks?)

Backward seeks from the end are 3 times slower than forward seeks.

open O, '+<:raw', '1GBx8.bin' or die $!;;

seek O, 0, 0; $t=time; seek O, $_*1000, 0 for 0 .. 8589934; print time
+-$t;;
7.61572408676147

seek O, 0, 0; $t=time; seek O, 1000, 1 for 0 .. 8589934; print time-$t
+;;
11.6447620391846

seek O, 0, 2; $t=time; seek O, -1000, 1 for 0 .. 8589934; print time-$
+t;;
11.6476919651031

seek O, 0, 2; $t=time; seek O, $_*-1000, 2 for 0 .. 8589934; print tim
+e-$t;;
23.074695110321
[download]

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority". I'm with torvalds on this

In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked

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Re^2: How smart is 'seek $fh, $pos, 0'? by choroba (Cardinal) on May 27, 2015 at 13:18 UTC
I'm getting 7, 8, 5, 12 on cygwin Perl 5.14.4, 25MB file. Update: Interestingly, I'm getting 7, 8, 6, 12 with 1GB file, too. Update #2: 7, 8, 9, 14 with 10GB. Update #3: back at home. My Linux desktop, 24GB file: `1.68571901321411 1.60926795005798 1.60942387580872 1.69600319862366` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l]
Re^3: How smart is 'seek $fh, $pos, 0'? by BrowserUk (Patriarch) on May 27, 2015 at 14:14 UTC
I'm getting 7, 8, 5, 12 on cygwin Perl 5.14.4, 25MB file. I did it on an 8GB file to (attempt) to prevent caching mucking with the numbers. And I'm sure that the values will vary depending upon the file (fragmented or not), device(disk/ssd/etc), version of perl, compiler/CRT, but the numbers are pretty consistent across all my devices and have been for several version of perl. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I'm with torvalds on this In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked	[reply]
Re^3: How smart is 'seek $fh, $pos, 0'? by BrowserUk (Patriarch) on May 27, 2015 at 15:20 UTC
Update: Interestingly, I'm getting 7, 8, 6, 12 with 1GB file, too. Still probably too small to prevent the entire file being cached. (Unless you have less that about 2GB ram?) Even so, I can't reason an explanation for why seek backwards relative would be faster than forwards. If you have the ability to run that utility that traces system calls (strace?), that might reveal something. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I'm with torvalds on this In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked	[reply]
Re^2: How smart is 'seek $fh, $pos, 0'? by MidLifeXis (Monsignor) on May 27, 2015 at 14:20 UTC
`Win32 strawberry-perl 5.18.2.1 - machine uses SSD 10.0880000591278 11.9660680294037 4.43941283226013 9.69746780395508` [download] `v5.8.8 built for PA-RISC2.0 - older, sloooowwwweeerrr machine, NAS 53.091873884201 57.2255661487579 42.3175899982452 50.95623087883` [download] --MidLifeXis	[reply] [d/l] [select]
Re^3: How smart is 'seek $fh, $pos, 0'? by BrowserUk (Patriarch) on May 27, 2015 at 14:35 UTC
As your relative seek backwards is faster than the absolute seek forwards, I'm guessing that the file you used fitted entirely in cache. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I'm with torvalds on this In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked	[reply]
Re^4: How smart is 'seek $fh, $pos, 0'? by MidLifeXis (Monsignor) on May 27, 2015 at 15:40 UTC
Given the hardware, that is entirely possible. Update: 20GB file (machine has 16 GB memory). END_POINT is the end of the loop on the calculations. `Using END_POINT => 20971520 24.7622640132904 29.1878440380096 29.0354490280151 43.3434360027313` [download] --MidLifeXis	[reply] [d/l]
Re^2: How smart is 'seek $fh, $pos, 0'? by Monk::Thomas (Friar) on May 27, 2015 at 13:29 UTC
Wow. Thanks for the benchmark.	[reply]